2013/3/11 Jeff Layton [email protected]:
On Thu, 28 Feb 2013 19:25:28 +0400 Pavel Shilovsky [email protected] wrote:
If O_DENYMAND flag is specified, O_DENYREAD/WRITE/MAND flags are translated to flock's flags:
!O_DENYREAD -> LOCK_READ !O_DENYWRITE -> LOCK_WRITE O_DENYMAND -> LOCK_MAND
and set through flock_lock_file on a file.
This change affects opens that use O_DENYMAND flag - all other native Linux opens don't care about these flags. It allow us to enable this feature for applications that need it (e.g. NFS and Samba servers that export the same directory for Windows clients, or Wine applications that access the same files simultaneously).
Create codepath is slightly changed to prevent data races on newely created files: when open with O_CREAT can return with -ETXTBSY error for successfully created files due to a deny lock set by another task.
Signed-off-by: Pavel Shilovsky [email protected]
fs/locks.c | 116 +++++++++++++++++++++++++++++++++++++++++++++++------ fs/namei.c | 44 ++++++++++++++++++-- include/linux/fs.h | 6 +++ 3 files changed, 151 insertions(+), 15 deletions(-)
diff --git a/fs/locks.c b/fs/locks.c index a94e331..0cc7d1b 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -605,20 +605,81 @@ static int posix_locks_conflict(struct file_lock *caller_fl, struct file_lock *s return (locks_conflict(caller_fl, sys_fl)); }
-/* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
- checking before calling the locks_conflict().
+static unsigned int +deny_flags_to_cmd(unsigned int flags) +{
unsigned int cmd = LOCK_MAND;if (!(flags & O_DENYREAD))cmd |= LOCK_READ;if (!(flags & O_DENYWRITE))cmd |= LOCK_WRITE;return cmd;+}
+/*
- locks_mand_conflict - Determine if there's a share reservation conflict
- @caller_fl: lock we're attempting to acquire
- @sys_fl: lock already present on system that we're checking against
- Check to see if there's a share_reservation conflict. LOCK_READ/LOCK_WRITE
- tell us whether the reservation allows other readers and writers.
- We only check against other LOCK_MAND locks, so applications that want to
- use share mode locking will only conflict against one another. "normal"
- applications that open files won't be affected by and won't themselves
*/
- affect the share reservations.
-static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl) +static int +locks_mand_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl) {
/* FLOCK locks referring to the same filp do not conflict with
unsigned char caller_type = caller_fl->fl_type;unsigned char sys_type = sys_fl->fl_type;fmode_t caller_fmode = caller_fl->fl_file->f_mode;fmode_t sys_fmode = sys_fl->fl_file->f_mode;/* they can only conflict if they're both LOCK_MAND */if (!(caller_type & LOCK_MAND) || !(sys_type & LOCK_MAND))return 0;if (!(caller_type & LOCK_READ) && (sys_fmode & FMODE_READ))return 1;if (!(caller_type & LOCK_WRITE) && (sys_fmode & FMODE_WRITE))return 1;if (!(sys_type & LOCK_READ) && (caller_fmode & FMODE_READ))return 1;if (!(sys_type & LOCK_WRITE) && (caller_fmode & FMODE_WRITE))return 1;return 0;+}
+/*
- Determine if lock sys_fl blocks lock caller_fl. FLOCK specific checking
- before calling the locks_conflict(). Boolean is_mand indicates whether
- we should use a share reservation scheme or not.
- */
+static int +flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl,
bool is_mand)I'm not sure you really need to add this new is_mand bool. Won't that be equivalent to (caller_fl->fl_type & LOCK_MAND)?
This function is already used by flock system call that can pass LOCK_MAND flag to caller_fl->fl_type. I don't want to affect existing flock behavior by introduing new denylocking strategy - so, we need to let flock_locks_conflict function know if we are in flock or open codepath - in open codepath it will call locks_mand_conflict to check if there is any other open that prevents us.
+{
/** FLOCK locks referring to the same filp do not conflict with * each other. */
if (!IS_FLOCK(sys_fl) || (caller_fl->fl_file == sys_fl->fl_file))return (0);if ((caller_fl->fl_type & LOCK_MAND) || (sys_fl->fl_type & LOCK_MAND))
if (!IS_FLOCK(sys_fl))return 0;if ((caller_fl->fl_type & LOCK_MAND) || (sys_fl->fl_type & LOCK_MAND)) {if (is_mand)return locks_mand_conflict(caller_fl, sys_fl);elsereturn 0;}if (caller_fl->fl_file == sys_fl->fl_file) return 0;
return (locks_conflict(caller_fl, sys_fl));
return locks_conflict(caller_fl, sys_fl);}
void @@ -697,14 +758,19 @@ static int posix_locks_deadlock(struct file_lock *caller_fl, return 0; }
-/* Try to create a FLOCK lock on filp. We always insert new FLOCK locks +/*
- Try to create a FLOCK lock on filp. We always insert new FLOCK locks
- after any leases, but before any posix locks.
- Note that if called with an FL_EXISTS argument, the caller may determine
- whether or not a lock was successfully freed by testing the return
- value for -ENOENT.
- Take @is_conflict callback that determines how to check if locks have
*/
- conflicts or not.
-static int flock_lock_file(struct file *filp, struct file_lock *request) +static int +flock_lock_file(struct file *filp, struct file_lock *request, bool is_mand)
Ditto here on the is_mand bool. I think you can determine that from request->fl_type. Right?
The same suggestions are applied to this place too.
{ struct file_lock *new_fl = NULL; struct file_lock **before; @@ -760,7 +826,7 @@ find_conflict: break; if (IS_LEASE(fl)) continue;
if (!flock_locks_conflict(request, fl))
if (!flock_locks_conflict(request, fl, is_mand)) continue; error = -EAGAIN; if (!(request->fl_flags & FL_SLEEP))@@ -783,6 +849,32 @@ out: return error; }
+/*
- Determine if a file is allowed to be opened with specified access and deny
- modes. Lock the file and return 0 if checks passed, otherwise return a error
- code.
- */
+int +deny_lock_file(struct file *filp) +{
struct file_lock *lock;int error = 0;if (!(filp->f_flags & O_DENYMAND))return error;error = flock_make_lock(filp, &lock, deny_flags_to_cmd(filp->f_flags));if (error)return error;error = flock_lock_file(filp, lock, true);if (error == -EAGAIN)error = -ETXTBSY;I think EBUSY would be a better return code here. ETXTBSY is returned in more specific circumstances -- mostly when you're opening a file for write that is being executed.
Yes, I agree. This work was done before the discussion in linux-cifs@ about a error code for STATUS_SHARING_VIOLATION.
locks_free_lock(lock);return error;+}
static int __posix_lock_file(struct inode *inode, struct file_lock *request, struct file_lock *conflock) { struct file_lock *fl; @@ -1589,7 +1681,7 @@ int flock_lock_file_wait(struct file *filp, struct file_lock *fl) int error; might_sleep(); for (;;) {
error = flock_lock_file(filp, fl);
error = flock_lock_file(filp, fl, false); if (error != FILE_LOCK_DEFERRED) break; error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);diff --git a/fs/namei.c b/fs/namei.c index 43a97ee..c1f7e08 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2559,9 +2559,14 @@ static int atomic_open(struct nameidata *nd, struct dentry *dentry, * here. */ error = may_open(&file->f_path, acc_mode, open_flag);
if (error)
if (error) { fput(file);goto out;}error = deny_lock_file(file);if (error)fput(file);out: dput(dentry); return error; @@ -2771,9 +2776,9 @@ retry_lookup: } mutex_lock(&dir->d_inode->i_mutex); error = lookup_open(nd, path, file, op, got_write, opened);
mutex_unlock(&dir->d_inode->i_mutex); if (error <= 0) {
mutex_unlock(&dir->d_inode->i_mutex); if (error) goto out;@@ -2791,8 +2796,32 @@ retry_lookup: will_truncate = false; acc_mode = MAY_OPEN; path_to_nameidata(path, nd);
goto finish_open_created;
/** Unlock parent i_mutex later when the open finishes - prevent* races when a file can be locked with a deny lock by another* task that opens the file.*/error = may_open(&nd->path, acc_mode, open_flag);if (error) {mutex_unlock(&dir->d_inode->i_mutex);goto out;}file->f_path.mnt = nd->path.mnt;error = finish_open(file, nd->path.dentry, NULL, opened);if (error) {mutex_unlock(&dir->d_inode->i_mutex);if (error == -EOPENSTALE)goto stale_open;goto out;}error = deny_lock_file(file);mutex_unlock(&dir->d_inode->i_mutex);if (error)goto exit_fput;goto opened; }mutex_unlock(&dir->d_inode->i_mutex); /* * create/update audit record if it already exists.@@ -2885,6 +2914,15 @@ finish_open_created: goto stale_open; goto out; }
/** Lock parent i_mutex to prevent races with deny locks on newely* created files.*/mutex_lock(&dir->d_inode->i_mutex);error = deny_lock_file(file);mutex_unlock(&dir->d_inode->i_mutex);if (error)goto exit_fput;opened: error = open_check_o_direct(file); if (error) diff --git a/include/linux/fs.h b/include/linux/fs.h index 7617ee0..347e1de 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1005,6 +1005,7 @@ extern int lease_modify(struct file_lock **, int); extern int lock_may_read(struct inode *, loff_t start, unsigned long count); extern int lock_may_write(struct inode *, loff_t start, unsigned long count); extern void locks_delete_block(struct file_lock *waiter); +extern int deny_lock_file(struct file *); extern void lock_flocks(void); extern void unlock_flocks(void); #else /* !CONFIG_FILE_LOCKING */ @@ -1153,6 +1154,11 @@ static inline void locks_delete_block(struct file_lock *waiter) { }
+static inline int deny_lock_file(struct file *filp) +{
return 0;+}
static inline void lock_flocks(void) { }
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